This study has attempted to apply several reproducible on-going immunochemical techniques for detection of circulating immune complexes to clinical problems. We have concentrated on conditions where some methodology has been available to identify the antigens present in such immune complexes, as well as the precise physical molecular profile of circulating complexes themselves. The appearance, quantitative amounts and molecular profiles of circulating complexes in patients with disseminated gonococcal infection, rapidly progressive glomeruloephritis, leprosy, acute rheumatic fever, the hemolytic-uremic syndrome associated with shigellosis and, most recently, Lyme arthritis have been examined. Additional work has focussed on specific mechanisms functioning to produce and cellular immune deficiency syndromes. In particular, attempts have been made to produce heterologous antisera which are capable of direct idenfification of suppressors T cells in peripheral blood and tissue, primarily using indirect immunofluorescence techniques. Attention has been directed at the profile of lymphocyte cell surface markers in patients with adult acquired agammaglobulinemia with particular reference to a small subset of T cells in such individuals which show Ia antigens on their surface . These studies appear to show an increase in Ia positive T-lymphocytes in adult agamma-glovulinemic subjects. It is not yet clear whether IA positive T cells represent a small population to T cells which are capable of mediating suppressor cell functions.